1 Optimization of baseline front end for a neutrino factory David Neuffer FNAL (August 19, 2009)

2Outline  Front End for the Neutrino Factory/MC  Study 2A – ISS baseline  Shorter front end example-  other variants (88MHz, Induction Linac)  Rf cavities in solenoids?  high gradient cavities may not work in ~2T fields  Options Use lower fields (B, V’)  Boulder Workshop Be cavities – magnetic focusing will not heat cavities enough for Breakdown ? R. Palmer  Need baseline design for IDS  need baseline for “5-year Plan”

3

4 IDS - Shorter Version  Reduce drift, buncher, rotator to get shorter bunch train:  217m ⇒ 125m  57m drift, 31m buncher, 36m rotator  Rf voltages up to 15MV/m (×2/3)  Obtains ~0.26 μ/p 24 in ref. acceptance  Similar or better than Study 2B baseline  Better for Muon Collider  80+ m bunchtrain reduced to < 50m  Δn: 18 -> m 500MeV/c

5 Buncher-Rotator settings  Buncher and Rotator have rf within ~2T fields  rf cavity/drift spacing same throughout (0.5m, 0.25)  rf gradient goes from 0 to 15 MV/m in buncher cavities  Cooling baseline  ASOL lattice  1 cm LiH slabs (3.6MeV/cell)  ~15MV/m cavities  also consider H 2 cooling  Simulated in G4Beamline  optimized to reduce # of frequencies  Shorter version has 20% higher gradient ASOL lattice

6Optimizations  Major uncertainty is high-gradient rf within solenoidal fields  V’ rf / B solenoid ???  Currently have B= 1.5 to 2T, V ’ = 12 to 15 MV/m  baseline frequency is ~200 MHz  Experiments have achieved~ 14 MV/m at 2.5-T  (~ 0.75-T at nearest thin Be window)  Solenoid near 201 MHz cavity

7 Variation on material, geometry  Surface/material changes maximum field  TiN coating (-> 30MV/m)  800 MHz  More improvement with ALD?  Open cell cavity  shows no dependence on B 

8 Solutions to possible rf cavity limitations  For IDS, we need an rf cavity + lattice that can work  Potential strategies:  Use lower fields (V’, B)  10MV/m at 1.5T?  Use non-B = constant lattices  alternating solenoid  Magnetically insulated cavities  Is it really better ???  Alternating solenoid is similar to magnetically insulated lattice  Shielded rf lattices  low B-field throughout rf  Use gas-filled rf cavities  same gradient with/without fields  but electron effects?

9 Current study  Change magnetic field, V’ rf to study limits  Use “short” front end for studies  Baseline had 2T solenoid in drift and buncher 0 to 15 MV/m rf  15 MV/m in rotator; 15 MV/m in cooler  vary rotator from 10 to 15 MV/m;  Cooler 12 to 18 MV/m 10 m~50 m FE Targ et Solenoid DriftBuncherRotatorCooler ~32m36m up to ~100m m p π→μ

10Results  Muons per 10 8-GeV protons Cooler/ Rotater is MV/m Variation is not strong; more rf still means more muons

11 Next try changing B  B= 1.33 T (~Study 2)  match into alternating solenoid  Tapering focus would help …

12 Change cavity material-Palmer  Tech-X rf breakdown modeling workshop Bob is convinced Be would solve the Front End Problem ? Needs experimental tests !!! B electrons 2R

13 Plan for IDS  Need one design likely to work for V rf /B-field  rf studies are likely to be inconclusive  Hold review to endorse a potential design for IDS  – likely to be acceptable (V rf /B-field)  April 2010 ?  Use reviewed design as basis for IDS engineering study